Currently, a housing of a mobile terminal includes forms of an integrated housing structure and a structure of “a TP (touch panel)/an LCD (liquid crystal display)+a middle frame+a back cover”. The housing structure of “a TP/an LCD+a middle frame+a back cover” greatly improves an aesthetic degree of the whole mobile terminal. Therefore, the housing structure is favored by more users. In addition, compared with a housing structure of the integrated housing structure type, in the housing structure of “a TP/an LCD+a middle frame+a back cover”, different materials can be selected for the back cover according to an actual situation. This can reduce costs. However, in the housing structure of “a TP/an LCD+a middle frame+a back cover”, the middle frame includes a metal outer frame of a frame structure, a tray that is internally connected to the metal outer frame and that is used to carry electronic parts and components, and a plastic outer frame disposed on an inner side of the metal outer frame. The metal outer frame is connected to the tray to form a middle board. A strength requirement of the middle board is relatively high. Therefore, in the prior art, the metal outer frame and the tray are connected together mainly in two manners: integrating, and fastening and connecting.
A main processing manner of integrating the tray and the metal outer frame includes numerical control machine processing and integrated die-casting. However, even though the numerical control machine processing has very high continuous workability, a high yield rate, relatively small space required by design, and a relatively exquisite appearance of a finished product, costs of the numerical control machine processing are excessively high. This does not help in controlling production costs. Even though costs of the processing manner of the integrated die-casting are relatively low, exterior parts of most of produced products have a severe disadvantage such as a hole or a flow mark, and a product qualification ratio is excessively low.
A main processing manner of fastening and connecting the tray and the metal outer frame includes point soldering, screw connection, bimetallic die-casting, and the like. The point soldering manner is to connect the tray and the metal outer frame through point soldering by using soldering tin. This solution does not affect an appearance structure of the middle frame. However, connection strength of the point soldering manner is relatively low, and product reliability is excessively low. When the tray is connected to the metal outer frame by using a screw, connection strength is high, product reliability is relatively desirable, and an appearance is relatively exquisite. However, a requirement on a size of a to-be-connected part is relatively high during the screw connection, and an external dimension of the mobile terminal is increased. This does not facilitate a miniaturization, lightening, and thinning design of the mobile terminal. The bimetallic die-casting solution has relatively high continuous workability, a relatively high yield rate, and relatively large space required by design. However, an appearance of a finished product has a flaw, and secondary processing is required. This requires more processes and increases costs.